Do Sex Hormones Influence the Immune System? OHSU Scientists Investigate

10/08/09  Portland, Ore.

Study begins as flu season returns

Researchers at Oregon Health & Science University hope to learn whether sex hormone levels can influence a woman's immune system function. Specifically, the scientists are looking for ways to address a universal problem: the weakening of the immune system as a person ages.

"In both men and women, immune system function declines as we age," said Ilhem Messaoudi, Ph.D., an assistant scientist in the Oregon National Primate Research Center and the Vaccine and Gene Therapy Institute at OHSU. "In women, we specifically witness this decline in the postmenopausal years. This leads us to investigate whether the absence of the female sex hormone estrogen may play a role in the weakening of a woman's disease defense system."

This theory has led Messaoudi and her colleagues to launch a new research project. They are currently enrolling postmenopausal women in a study that will track immune system function and its relationship to estrogen levels. To accomplish this, the scientists are studying two groups of women: postmenopausal women who are receiving estrogen replacement therapy and post menopausal women who are not.

To compare immune system function in these two groups, both groups will receive flu vaccinations. In the following days, researchers will track the immune system's response in both groups. Specifically, they will investigate the body's T cell response to the vaccine and the production of antibodies.

Previous studies in animals conducted by Messaoudi and colleagues have suggested that there is indeed a connection between estrogen and immune system function. To conduct these animal studies, the scientists induced menopause by removing the ovaries from a small group of female monkeys – the same process used to spay dogs. They then compared immune system function to animals with ovaries. This comparison revealed dramatically reduced T cell response and dramatically reduced antibody production in the animals lacking ovaries.

"We believe there is a strong chance that our human studies will show the same to be true," added Messaoudi. "One important note is that the study is not being conducted to either encourage or discourage women from receiving hormone replacement therapy (HRT). The controversy surrounding the potential side effects of HRT is well-publicized. Instead, we are attempting to learn about the fundamental connections between sex hormones and the immune system for the advancement of scientific knowledge and perhaps for the development of new vaccination strategies that do not pose any additional risk."

Currently, the researchers are looking for women to take part in this study. Participants must be at least two years post-menopause, using estrogen-only hormone replacement therapy and willing to get a flu shot this year.

This research is funded by The Center for Gender Based Medicine. The previous nonhuman primate studies were funded by the Medical Research Foundation of Oregon and the Oregon National Primate Research Center.

Those wishing to obtain more information about this study can call 503 494-3666.